<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>表格3</title>
</head>
<body>
  <table align="center" border="1" width="1000">
    <tr>
      <td>A1</td>
      <td>A2</td>
      <td>A3</td>
      <td>A4</td>
    </tr>
    <tr>
      <td colspan="4">
        <table width="1000" border="1">
          <tr>
            <td>B1</td>
            <td>B2</td>
            <td>B3</td>
          </tr>
        </table>
      </td>
    </tr>
    <tr>
      <td>C1</td>
      <td>C2</td>
      <td>C3</td>
      <td>C4</td>
    </tr>
  </table>
</body>
</html>